Coal slurries are made up of very small particles of coal suspended in water. The particle diameter is typically in the range of 30-90 μm. These slurries present disposal problems for coal mines as well as creating environmental hazards. The purpose of the present invention is to provide an economical method for dewatering the coal slurry in order to be able to substantially reduce or eliminate the waste problem and to be able to put the dried coal particles to use for various beneficial purposes.
Prior art arrangements for dewatering of slurries involve filtration, primarily obtained by passing a pair of filtering cloths and belts through a system of rollers. The feed slurry is introduced between the two filter cloths, which are supported by perforated belts that allow water to fall through the belts. As the belts pass through the rollers, the water is squeezed out of the slurry. After the last set of rollers, the belts are separated and the filter cake is scraped off before the belts are washed by means of water sprays positioned on the return section of the belts.
Since the slurry is in direct contact with the filtering cloths, the cloths tend to become clogged with solids. Eventually, the cleaning with the water sprays fails to clean the filtering cloths sufficiently and they become blinded and must be replaced. A substantial amount of clean water is used for washing the filtering cloths, and this water becomes contaminated with the residual slurry on the filtering cloths and creates an additional waste disposal problem.